1. Field of the Invention
The present invention relates to a paper post-processing apparatus and image forming system equipped with a paper turn-over unit.
2. Description of the Related Art
An image forming system is provided which allows various types of post-processing to be performed on paper by a post-processing apparatus after an image is formed on the paper by an image forming apparatus.
Some paper used in image formation and post-processing has different textures on front and back sides, for example, with the front side being glossy and back side being non-glossy, and there is sometimes a desire to obtain an output in which all sheets are oriented in the same direction with their front side turned in one direction and their back side turned in the other direction in a binding process and the like.
For example, Japanese Patent Laid-Open No. 2011-73869 proposes an image forming apparatus, post-processing apparatus, and image forming system which perform display control so as to display a message, asking a user to place a cover anew in a direction opposite a direction in which the cover is placed in a binding processing mode.
Also, Japanese Patent Laid-Open No. 2007-320713 proposes a sheet folding apparatus and image forming system which turn over paper using a paper turn-over unit of an insert apparatus according to a folding mode setting in post-processing when inserting insert paper.
However, when plural post-processors are provided, if post-processing which involves turning over a paper is carried out in a post-processor of a preceding stage, there is a problem in that the front side and back side of the output paper obtained in a post-processor of a succeeding stage are reversed depending on whether the post-processor of the preceding stage is used or not.
For example, a post-processor which performs a creasing process is known as a post-processor which includes a paper turn-over unit. In this case, the paper is creased by being passed through an inversion path and after the creasing, the paper is transported downstream with its front and back sides reversed from when introduced into the post-processor.
Post-processing which involves a creasing process in this way is sometimes used in combination with other types of post-processing. For example, there is demand to form lines on a cover before case binding using a creasing unit in order to make it easy to fold a corner between cover and spine in case binding. In so doing, if the papers are turned over only when creases are provided, the front and back sides of the cover are reversed depending on whether creases are present or absent. That is, in case binding, the side on which a fold is formed is reversed depending on whether creases are present or absent.
Paper turn-over operations, which involve productivity reduction and paper size constraints, are desirably avoided unless necessary. If paper is not turned over by a paper turn-over unit, it becomes necessary instead for the user to turn over and set the paper contained in a paper feed cassette.
In contrast, Japanese Patent Laid-Open No. 2011-73869 described above simply displays a message on a panel, prompting the user to turn over the paper, but does not reduce the labor of turning over the paper.
Also, since Japanese Patent Laid-Open No. 2007-320713 assumes the use of the paper turn-over unit of the insert apparatus, the paper cannot be turned over if such an apparatus is not available. Also, it is only possible to reverse the front and back sides of the insert paper, and it is not possible to reverse the front and back sides of the paper subjected to post-processing automatically according to details of post-processing.